Liver tests are blood tests that represent a noninvasive way to screen for the presence of liver disease (for example, viral hepatitis in donated blood) and to measure the severity and progress of liver disease as well as the response to treatment.
Laboratory tests are generally effective for the following:
Detecting liver inflammation or damage
Assessing how well the liver is functioning at making proteins ("synthetic" function)
Assessing how well bile is being processed and transported through the liver, gallbladder, and biliary system
Assessing the severity of liver injury
Monitoring the course of liver diseases and a person's response to treatment
Refining the diagnosis
Liver tests are done on blood samples and measure the levels of enzymes and other substances produced by the liver. These substances include
Alanine aminotransferase (ALT)
Albumin
Alkaline phosphatase (ALP)
Alpha-fetoprotein (AFP)
Aspartate aminotransferase (AST)
Bilirubin
Gamma-glutamyl transpeptidase (GGT)
Lactate dehydrogenase (LDH)
5’-Nucleotidase
Prothrombin time (PT) and international normalized ratio (INR)
Partial thromboplastin time (PTT)
Levels of some of these substances measure the presence and degree of liver inflammation and hepatocyte injury (for example, ALT, AST). Levels of other substances measure how well the liver performs its normal functions of making proteins (for example, albumin), processing, and secreting bile (for example, bilirubin). Some of these values can be higher than normal in people with disorders not related to the liver.
Broadly speaking, liver injury and inflammation are reflected by the ALT and AST, the ability of the liver to make proteins by albumin and PT, and the ability to process and/or transport bile by the bilirubin, GGT, 5'-nucleotidase, and ALP. There is some overlap between these tests.
The prothrombin time (PT) is used to calculate the international normalized ratio (INR). Both the PT and the INR are measures of the time needed for blood to clot (the liver synthesizes some proteins necessary for blood clotting, called blood clotting factors). An abnormal PT or INR result can indicate an acute or chronic liver disorder. In both acute and chronic liver disorders, an increasing PT or INR typically indicates progression to liver failure.
To determine the possible cause of any liver test abnormalities, the doctor will also take a history and may conduct imaging studies and/or do a liver biopsy.
